Print processes compatible with thermoforming processes are known in the art. Conventional digital printers operate by scanning an array of printheads repeatedly across the media web while indexing the travel of the web, i.e., similar to the raster like functioning of traditional ink jet printers. This conventional print process is extremely time consuming in a manufacturing environment in which printed rolls must be delivered to one or more thermoforming presses. Often, the time required to print greatly exceeds the time necessary for thermoforming.
The following are two examples of printing systems used with thermoformable materials. Electronics For Imaging's VUTEk GS Pro-TF Series digital inkjet printer can allegedly produce custom formed signs, packaging, POP displays, vending panels and other thermoforming applications. Similarly, FUJIFILM's Acuity Advance Select is a flatbed inkjet printer used to produce printed thermoforms. Unfortunately, both systems suffer from the drawback of utilizing a scanning printhead which severely limits system throughput, e.g., FUJIFILM's system advertises throughput up to only 32 m2/hr.
Further complicating the process of printing on thermoformable material is the optical characteristics of that material. Many thermoformable materials are transparent, which is a desirable characteristic when being used to hold product that consumers wish to see prior to purchase, e.g., strawberries in a clear plastic container. Clear materials pose a challenge for printing conventional CMYK images (cyan, magenta, yellow and key (black)) since incident light will transmit through the ink. To improve visibility, it is common to print a CMYK image onto a white background having high reflectance. In order to maximize the usefulness of a printing system and minimize costs, preferably the white background is created using the same printing process used for CMYK printing.
Subsequent to printing on the thermoformable material, the material is rewound into a roll. Due to the thermoformability which requires low cross-linking in the cured inks, e.g., ultraviolet (UV) cured inks, it has been found that these inks are prone to “roll offset” failure, also known as “set-off” in the industry. The white ink and/or the CMYK images may transfer from the top surface of the thermoformable material to the bottom surface of the portion of the roll positioned directly adjacent to images in a process commonly known as setting off. In other terms, the printed images, while held in rolled form, migrate from intended locations to unintended locations, thereby resulting in unacceptable print quality. Because of the offset, commercial thermoforming printers typically adopt a wide-format, where the UV cured ink is kept exposed to air before thermoforming. The foregoing greatly limits the productivity for a thermoforming product.
The present disclosure addresses a system and method for high throughput printing on thermoformable substrates without unacceptable setting off of printed images. In other terms, a high-volume roll-to-roll format system for thermoforming applications is needed.